Electric insulator and method of making same



R. B. WHITE ELECTRIC INSULATOR AND METHOD OF MAKING SAME July 1, 1958 Filed Sept. 24, 1953 INVENTOR.

I I0 ROGER B. WHITE A TTORNE Y United States Patent M ELECTRIC INSULATOR AND METHOD OF MAKING SAME Roger B. White, Cleveland, Ohio, assignor to The Glastic Corporation, Cleveland, Ohio, a corporation of Ohio Application September 24, 1953, Serial No. 382,078

4 Claims. (Cl. 174138) This invention pertains to the art of electric insulators and, more particularly, to an electric insulator of the standoff type and the method of manufacturing same.

Standoff insulators of the type to which this invention pertains are normally employed to support heavy mechanical members relative'to a base or support while, at the same time, electrically insulating same and the invention will be described with particular reference to such an insulator, although it will be appreciated that it has broader applications.

Such standoif type insulators normally consist of a mass of electrical insulating material either molded or machined to shape from electrical insulating material and having means for fastening thereto such as metallic inserts molded into the insulating material by which a mechanical connection can be made to the insulator. These means are normally supported in the insulator at spaced points so as to be in electrically insulated relationship.

.These insulators, as has been inferred, in addition to the insulating function implied by their name, must also support heavy mechanical loads which impose high stresses on the insulating material. Accordingly, special constructions of the insulator are required together with a high quality of the insulating material in order that the insulator will not fracture in service.

The present invention contemplates an electrical insulator of the general type referred to which has a minimum bulk, a minimum weight of raw materials and a maximum strength, together with high electrical insulating properties.

In accordance with the present invention, the insulator is comprised of a mass of electric insulating material made up of a plurality of generally continuous strands of electrically insulating fibrous material thoroughly impregnated with a hardened, thermosetting, liquid resin and spaced means for making a mechanical connection between the insulator and a base or article to which it is to be attached.

The fibrous material, as indicated, must be of an electrical insulating type and must also have relatively high, unit area tensile strength while being quite flexible and able to bend prior to the application of the hardened thermosetting, resin material. acteristics normally required to carry out the invention.

The thermosetting resin should be of a type which readily wets the surface of the fibrous material and can form an even tenacious bond therewith in the hardened state. Polyester-type resins have been found quite satisfactory and have the required electrical insulating characteristics.

The means for making the mechanical connection may either be openings such as threaded openings in the body of the material into which metallic members can be in serted or the means can be metallic members such as threaded sleeves or threaded bolts between the fibrous strands and molded into the insulator as an integral part thereof.

Fiber glass has the char-' 2,841,636 Patented July 1, 1958 The insulator may be solid in cross section but it is preferred that it be in theshape of a sleeve or tube with the fibrous material running continuously in a peripheral direction either straight; that is, with all strands directly in parallel relationship, or in random; that is, with the individual strands continuously crossing and recrossing each other.

In accordance with the invention, the insulator may be manufactured by combining a plurality of strands of fibrous material such as glass fiber, each strand being made up of a plurality of fine, small-diameter filaments, impregnating the combined strands, winding these impregnated strands onto a mandrel and heating the re sultant coil to cause the resinous material to set. Thereafter, the mandrel is removed. The insulator may be externally shaped such as by using guides or ends on the mandrel and/or mold members may be moved into physical and pressure engagement with the external sides of the insulator prior to and during the heating operation.

The principal object of the invention is the provision of a new and improved electrical insulator which has a maximum strength, is relatively cheap to manufacture, provides a maximum of electrical insulation and is easily and cheaply manufactured.

Another object of the invention is the provision of a new and improved electrical insulator made up of a mass of fibrous material running generally in the same direction and impregnated with a hardened thermosetting resinous material so as to have a maximum of strength or a minimum of weight.

Another object of the invention is the provision of a new and improved electrical insulator in the shape of a sleeve or tube having the walls thereof comprised of a generally solid mass of peripherally extending fibrous material impregnated with a thermosetting resin.

Another object of the invention is the provision of a new and improved method of manufacturing an electrical insulator comprising coiling an indeterminate length of glass fibrous material impregnated with a liquid thermosetting resin about a mandrel to provide a generally solid body of fibrous material, heating such mass to cure the and combination of steps and certain parts and combination of parts, a preferred embodiment of which will be described in this specification and illustrated in the accompanying drawing which forms a part hereof, and wherein:

Figure 1 shows a perspective view of an electrical insulator with portions partly broken away to illustrate a preferred embodiment of the invention;

Figure 2 is a somewhat schematic view of the insulator of Figure 1 in the process of manufacture and illustrating a preferred embodiment of the method of manufacture;

Figure 3 is a fragmentary top elevational view of Figure 2 showing the insulator in the process of manufacture;

Figure 4 is a side cross-sectional view showing a further step in the process of manufacture;

Figure 5 is a cross-sectional view of Figure 1 taken approximately on the line 44 thereof and showing an alternative embodiment of the invention; and

Figure 6 is a top elevational view of Figure 1 showing a still further alternative embodiment of the invention.

Referring now to the drawings wherein the showings are for the purposes of illustrating the invention only and not for the purposes of limiting same, the electrical insulator shown in Figure l is generally in the shape of a sleeve or tube 10 defining an internal passage 11 and having means 12 for mechanically connecting the insulator to external mechanical and electrical means.

The passage 11 is shown as being open at both ends and having generally a rectangular or square cross secconvenience and, obviously, may be either round, rectangular or otherwise as desired. Also, it is not necessary that the passage 11 be open at both ends and, if desired, it could be open at only one end or closed at both ends. In the latter case, however, it will be appreciated that it would be difficult to remove the core or mandrel used to shape the passage 11. It will also be apprcciated that the passage 11 could be eliminated entirely and the insulator made of a solid body from the impregnated fibrous material to be subsequently described.

Themeans 12 for attaching the insulator to external mechanical members in the embodiments shown is comprised of threaded bolts 13 extending through the sides of the tube at spaced points. These bolts 13 may have any desired shape, either being purely cylindrical or they may be provided with heads 14 embedded in the wall for the purpose of giving improved mechanical support of the bolts in the side walls of the tube.

Obviously, the bolts 12 could take any desired shape or they could be eliminated entirely and openings simply provided in the walls of the tube adapted to receive metallic members which could be fastened to the side walls of the tube 19 in any known manner. If desired, the means 12 could include clamping means fastened over the ends of the tube 19.

In accordance with the invention, the side walls of the tube 10 are made up of a plurality of tiny glass filaments 15 of indeterminate length, all extending in generally parallel relationship in a peripheral direction around the tube 19 and all impregnated by a hardenedthermosetting resinous material. 3

By a plurality is meant a sufiicient number of. fiber filaments that the entire side walls of the tube 10 will be generally solid with the glass filaments, such filaments having tiny spaces at random in between, which spaces will be completely filled with the resinous material.

By an indeterminate length is meant any length of glass filament required to make a continuous strand'of filament generally all in parallel relationship of an unlimited length. Normally, such filaments will have a length equal to the lengths of the strands, although the invention does not exclude filaments of lengths down to, say, one or two inches providing that such filaments can be incorporated into a continuous strand of unlimited length, either by weaving or by the use of adhesive-like materials.

By the term parallel relationship of the individual glass filament is meant that the glass fibers will extend in a generally peripheral direction around the tube but the invention does not exclude fibers which extend in a relatively random relationship so that they continually lap and overlap each other.

It will be noted from Figure 1 that the fibers while being generally parallel and extending peripherally around the tube 10 must diverge generally to make a space for the bolt 13 which will thus tend to leave a slight space on each side of the bolt 13 in the direction of the length of the filament which will not be filled with the glass fibers. However, the thermosetting resinous material fills this space being squeezed thereinto by the molding process. 7

The thermosetting resinous material employed may be as desired but, in the preferred embodiment, a polyester type therrnosetting resin is employed. However, allyl alcohols, melamine or urea type resins may also be employed. It is preferred that such resins be employed in the liquid state in order that the glass fibers may be readily and quickly impregnated by the resinous material.

7 The insulator shown in Figure 1 may be manufactured by a number of diiferent processes. A preferred embodiment of the process is illustrated in Figures 2 through 4. In Figure 2, there is shown three spools '20 on which are coiled continuous lengths of strands of glass fiber, each strand being made up of a plurality of individual filaments of glass. While the strands are continuous in l length for the entire spool, the individual filaments may have a length much shorter than the length of the strand. The individual strands indicated generally by the reference character 21 are advanced through a guide 22 which brings all of the strands in a group generally in the form of a rope indicated by the reference character 23. This rope 23 is then advanced over a second guide 24 shown in the shape of a roller into a bath 26 of liquid resin material of the thermosetting type, preferably a polyester resin. A pair of guide members 27 are employed to hold the rope 23 below the surface of the resinous material 26. The impregnated rope indicated by the reference numeral 29 emerges from the bath 26 and passes through a sizing die 28 which scrapes or otherwise removes the excess resin 26 and allows it to drip back into the bath. The impregnated rope 29 then passes over a roller 31 where it is wound on a mandrel 34 having a crosssectional shape of that desired for the final insulator.

' This mandrel 34 is continuously rotated and draws the strands 21 from the spools 29 through the process just described and coils the impregnated rope 29 on its outer surface. The rotation of the mandrel 24 is continued until the desired wall thickness of the insulator is coiled onto .the mandrel 34.

Either prior to or after the coiling operation is com-.

menced, the bolts 13 are positioned on the mandrel in any suitable manner and the coiling then continued, it being appreciated that the impregnating rope 29 will be advanced axially back and forth along the mandrel so that an even and uniform layer of impregnated fibers will resuit on the mandrel 34. In the preferred embodiment it is' contemplated that endsor guides 36 of thin fibrous material be mounted on the mandrel 3 4 for the purpose of shaping the ends of the tube 10 and accurately controlling the ultimate length of the tube 16 and, thus, this dimension of theinsulator.

When the desired wall thickness is obtained, :the' impregnate'd rope 29 is cut off and the mandrel with the end guides 36 is moved into a molding machine shown somewhat schematically in Fig Ie 4. The'molding machine shown is comprised of two horizontally movable mold members at of a width to just fit between the end guides 36 and an over-all height generally equal to the height of the ultimate insulator to be made. r

The machine is also comprised of a pair of vertically movable mold members 41 each having a vertical bore therein 42 of a dimensionto receive the bolts 13. These mold members 40 and 41 are moved into engagement with the external surface of the coiled impregnated rope 29 to shape the material to theultimate desired shape of the insulator. Varying degrees of pressure may be applied as desired. These mold, members are preferably heated to elevated temperatures so as to'accelerate the curing of the resinous material. In a like manner, the mandrel 34 may also be heated by any suitable or known means so that a curing action takes place both from the insideout and the outsidein of the insulator. The glass fiber material and the polyester resin are both excellent electrical insulating materials and an insulator'results having excellent electrical characteristics. In a like manner, the glass fiber material when'impregmated with such a resin has very substantial mechanical strengths and an insulator, results having a very high strength which is one of the prime requirements of such insulators.

.In particular, the strength of the insulator in the direction of the glass fibers is very great. It will be somewhatless in a direction" transverse to the direction of the glass fibers but there is generally sufficient overlapping of the glass fibers even when wound in a generally parallel direction that the stresses in the insulator are distributed from one filament to adjacent filaments. This strength seems to result even though the fibers do not fit tight on each side of the bolt 13 in the longitudinal direction.

If a maximum strength in all directions is required,

a the modifications shown in Figures and 6 may be employed.

Referring now to Figure 5, it is here shown that the fibers 15, instead of being wound in generally parallel relationship, are Wound so as to continually overlap each other and specifically the fibers approach the bolt 13 at an angle relative to the length of the insulator, bear against the bolt 13 and are further angled across the length of the insulator so as to substantially fill the space on all sides of the bolt 13. It will also be noted that the strands as shown in Figure 5 continuously overlap and run in a criss-cross direction so that any forces from any direction imposed on the bolt 1.3 can be uniformly resistant by a generally uniform cross section of glass fiber filaments.

Figure 6 shows a still further modification of the preferred embodiment. In this embodiment of the invention, the bolts 13 prior to being mounted on the mandrel 34 first have a mat 45 of glass cloth placed against the head. Then the impregnated rope 29 is coiled over this mat 45 as above indicated until substantially the ultimate desired thickness of the insulator is obtained. Thereafter, a second glass mat 46 having an opening to receive the bolt 13 is placed thereover and the ultimate molding operation then carried out. It will 'be appreciated, however, that after the mat 46 is placed in position, additional turns of the impregnated rope 29 could be coiled over the mat 46. In any event, the glass mat tends to distribute any stresses and strains placed on the bolt 13 equally throughout the body of the insulator shown.

Thus, it will be seen that preferred embodiments of the invention have been described which accomplish all of the objects heretofore set forth and others and provides an electrical insulator of extreme mechanical strength and high electrical insulating qualities.

in accordance with the patent laws, a preferred embodiment of the invention has been described. Obviously, the invention may take physical form in other radically diiferent appearing embodiments which will occur to others upon a reading and understanding of this specification. It is my intention to include all such modifications insofar as they come within the scope of the appended claims.

Having thus described my invention, 1 claim:

1. An electrical insulator comprising a hollow sleeve having the side walls thereof made up of a plurality of glass fibers running peripherally of the sleeve and a hardened thermosetting resinous material thoroughly impregnating said fibers and means for making a mechanical connection to said insulator, said means constituting a threaded member embedded in a side wall between adjacent portions of said glass fiber.

2. An electrical insulator comprising a sleeve with the side walls thereof made up of a plurality of continuous glass fibers running generally peripherally thereof and impregnated with a hardened thermosetting resin and means in the form of a bolt embedded in at least one of the walls of said tube and extending therebeyond for making a mechanical connection to said insulator said bolt extending between the glass fibers and transversely to the wall and the axis of the sleeve.

3. The combination of claim 2 wherein glass mats are provided extending radially from said bolt and commingled with said glass fibers.

4. An electrical insulator comprising a member in the shape of a sleeve, the side walls thereof made up of a plurality of glass fibers running generally peripherally thereof, means for making mechanical connection to said insulator comprising a pair of spaced bolts embedded in the walls of said sleeve, said glass fibers curving at least part way around said bolt whereby to provide a criss-cross pattern of fibers to form the wall of said sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 1,944,508 Gubler Jan. 23, 1934 2,025,540 Langley Dec. 24, 1935 2,431,883 Morton Dec. 2, 1947 2,441,309 Cook May 11, 1948 2,467,999 Stephens Apr. 19, 1949 2,594,838 Alexander et a1 Apr. 29, 1952 2,615,954 Mungovan et al. Oct. 28, 1952 2,661,390 Gelpi Dec. 1, 1953 2,718,583 Noland Sept. 20, 1955 FOREIGN PATENTS 734,717 France Oct. 27, 1932 

1. AN ELECTRICAL INSULATOR COMPRISING A HOLLOW SLEEVE HAVING THE SIDE WALLS THEREOF MADE UP OF A PLURALITY OF GLASS FIBERS RUNNING PERIPHERALLY OF THE SLEEVE AND A HARDENED THERMOSETTING RESINOUS MATERIAL THOROUGHLY IMPREGNATING SAID FIBERS AND MEANS FOR MAKING A MECHANICAL CONNECTION TO SAID INSULATOR, SAID MEANS CONSTITUTING 